Gas generating compositions

ABSTRACT

A gas generating composition having as ingredients an alkali or alkaline earth metal azide, an oxidizing compound, an oxide such as silica or alumina, and optionally, a metal such as silicon or aluminum. The composition is useful as a source of gas to inflate bags used as restraint systems for the protection of automobile passengers.

United States Patent Sidebottom May 13, 1975 GAS GENERATING COMPOSITIONS [56] References Cited [75] Inventor: Eric William Sidebottom, Otterburn UNITED STATES PATENTS Heights, Q Canada 2,981,616 4/1961 Boyer 149/35 [731 2964292 4:22: ::1;"::,:%i';;;--

112/22 9 Montreal Quebm Canada 3,797,854 3/1974 POOle et al 149/35 x [22] Filed: July 2, 1973 Primary ExaminerStephen J. Lechert, Jr. [2]] Appl' 375654 Attorney, Agent, or FirmAlexander O. Mclntosh [30] Foreign Application Priority Data [57] ABSTRACT July 24, i972 United Kingdom 34481/72 A gas generating composition having as ingredients an alkali or alkaline earth metal azide, an oxidizing com- [52] US. Cl. 149/6; 149/35, 149/37, pound, an Oxide such as silica or alumina, and option 149/40; 149/41; 149/42; 149/43; 149/45; ally, a metal such as silicon or aluminum. The compo- 149/75 149/77 sition is useful as a source of gas to inflate bags used Int. I as restraint Systems f the protection of automobile [58] Field of Search 149/6, 35, 37, 75, 40,

passengers.

8 Claims, No Drawings GAS GENERATING COMPOSITIONS This invention relates to a composition of matter suitable for generating gases.

As a safety measure, inflatable restraint systems have been devised to protect the passengers of automobiles in the event of collision. These systems commonly consist of a bag located in front of the passengers which is caused to inflate in response to rapid decelaration of the automobile.

It is known to inflate the bag through the action of compressed gas released from a storage vessel. However, the use of compressed gas for this purpose entails certain disadvantages. A large heavy-walled vessel is required to store the gas under a pressure of about 3,000 pounds per square inch. It is also necessary to ensure that the gas storage vessel remain sealed over long period of time, ready for service in case of an accident.

It is also known to inflate the bag through the action of gas developed by a burning propellant or pyrotechnic composition. Block powder has been employed as the gas generating composition but has the disadvantage that the products of combustion are noxious. Compositions containing alkali metal azides have advantages as means for gas generation since the product of combustion is mainly nitrogen gas, However, a composition consisting of an alkali metal azide and an oxygencontaining oxidizing compound produces, in addition to nitrogen, a certain amount of toxic, corrosive alkali metal oxide, Such a composition is disclosed in US. Pat. No. 2,981,616 for use as a source of gas for pressurizing rocket propellant tanks. Pyrotechnic compositions containing an alkali metal azide, oxidizing compound and a fuel such as boron or silicon are disclosed in US. Pat. No. 3,122,462. When used as sources of gas, however, these pyrotechnic compositions, depending upon the proportions of the ingredients, may exhibit a high burning rate, approaching detonation.

A gas generating composition suitable for inflating an automobile restraint system has now been found which avoids the disadvantages of prior art propellant and pyrotechnic compositions. The novel composition contains an alkali metal or alkaline earth metal azide, an oxidizing compound and an oxide of silicon, aluminium, titanium, tin or zinc with or without admixture with silicon, aluminum, titanium, tin or zinc metal, said oxide, and metal if present, being in amount sufficient to react with metallic oxides produced during the decomposition of the azide. The composition produces nitrogen gas at a rate suitable for inflation of an automobile restraint bag and the solid products of gas forming reaction are non-toxic and non-corrosive.

It is thus the primary object of the invention to provide a gas generating composition wherein the products of the gas generating reaction are non-toxic and noncorrosive. Additional objects will appear hereinafter.

The gas generating composition of this invention comprises l an azide of an alkali metal or an alkaline earth (2) an oxidizing compound in proportion sufficient to react completely with said azide with the liberation of nitrogen gas therefrom, and (3) an oxide selected from the group consisting of silicon oxide, aluminum oxide, titanium oxide, tin oxide and zinc oxide, with or without admixture with a metal selected from the group consisting of silicon, aluminum, titanium, tin

and zinc, in proportion sufficient to react with the metallic residue of the reaction between (1) and (2).

The use of a mixture of an oxide and a metal as ingredients of the composition provides a means of adjusting the burning rate. Compositions containing only oxide as ingredient (3) burn more slowly than compositions having only metal as ingredient (3). When (3) is a mixture of silica and silicon, variation of the proportions of these two components provides a range of burning rates extending from about 1 10 milliseconds with silica only to about 1 1 milliseconds with silicon only, depending on the size and configuration of the propellant mass.

The ingredients of the gas generating composition may be mixed together in the form of solid particles and ignited by means of a hot wire or a squib. Alternatively, the composition may be employed in two separate portions, a first portion comprising the azide and the oxidizing compound, and a second portion comprising the metallic oxide. The second portion will then be placed as a sheath about the first portion, or be placed in the outlet zone of the vessel carrying the gas generating composition.

As is known in the art, the gas generating composition will be enclosed in a vessel that communicates with the inflatable bag of the restraint system. Normally a baffle and/or filtering device will be positioned in the gas duct between the gas generating vessel and the inflatable bag for the purpose of restricting the flow of solid products into the bag.

The reaction of the gas generating composition can be represented by the equation:

2NaN $10 o N21 SiO 6N2 where the azide is sodium azide, the oxide is silica and oxygen is obtained from a suitable oxidizing compound. In the case where the azide is sodium azide, the oxide is silica andpotassium perchlorate is the oxidizing compound the equation will be:

When a mixture of silica and silicon is employed as ingredient (3) the reaction can be represented by the equation:

SNaN: mSi (4m)SiO (1+0.5m) KClO,

4Na SiO (1+0.5m)KCl 12N The silicate formed will depend upon the composition of the azide employed. With barium azide, for example, the silicate will be BaSiO It also can be expected that in the presence of the oxidizing compound the reaction may produce complex silicates.

Suitable azide ingredients of the gas generating compositions of this invention are lithium azide, sodium azide, potassium azide, rubidium azide, cesium azide, calcium azide, magnesium azide, strontium azide and bar- .ium azide.

, Oxidizing compounds suitable as ingredients of the gas generating compositions include metal peroxides such as sodium peroxide, potassium peroxide, rubidium peroxide, cesium peroxide, calcium peroxide, strontium peroxide, and varium peroxide; inorganic perchlorates such as lithium perchlorate, sodium perchlorate, potassium perchlorate, rubidium perchlorate, magnesium perchlorate, calcium perchlorate, strontium perchlorate, barium perchlorate, ferric perchlorate and cobalt perchlorate; and metal nitrates such as lithium nitrate, sodium nitrate, potassium nitrate, copper nitrate, silver nitrate, magnesium nitrate, barium nitrate, zinc nitrate, aluminum nitrate, thallium nitrate, stannic nitrate, bismuth nitrate, manganese nitrate, ferric nitrate, ferrous nitrate and nickel nitrate.

Oxides suitable as ingredients of the gas generating compositions include silicon dioxide (silica) aluminum oxide, titanium dioxide, tin oxide, and zinc oxide. Metals suitable as ingredients of the compositions include silicon, aluminium, titanium, tin and zinc.

It has been found that the impact sensitivity of the composition is reduced by including as ingredient, fumed silica coated with a water repellent such as a silane. This type of hydrophobic silica is described at page 39 of the Sept. 8, 1971 issue of Volume 109 of Chemical Week. The preferred portion of coated fumed silica is an additional 2 percent by weight. However, the coated fumed silica may replace the total oxide content of the composition.

The proportions of the azide and oxidizing compound are chosen so that the azide will be completely reacted to form gaseous nitrogen. Azides are toxic materials and it is undesirable to inject unreacted azide into the inflatable restraint bag. The proportion of oxide and when present the metal is chosen so that the metallic residue of the reaction between the azide and the oxidizing compound will react to form the non toxic solid compounds. When the oxide is silica and the metal silicon, the compounds formed will be silicates. In the case of other oxides and metals there will be formed oxygen-containing compounds such as aluminates, titanates, etc.

The ingredients of the gas generating composition are employed in particulate form. Although particle size is not apparently critical, it is convenient to employ material in the particle size less than 100 mesh Tyler screen size.

The gas generating compositions of the present onvention provides means for generating non-toxic gas by means of a reaction that produces non-toxic solid products.

The invention is additionally illustrated by the followmg Examples but its scope is not limited to the embodiments shown therein.

EXAMPLE 1 Three 40 gram charges of a composition containing sodium azide, silicon dioxide and potassium perchlorate in the molar proportions 814:1 were placed in canisters and ignited in a field test using a No. 8 electric blasting cap to initiate ignition. The material burned in slightly less than 1 second.

EXAMPLE 2 One gram charge of the above formulation was ignited by an S1 19 squib. Material required about 3 seconds for complete combustion.

EXAMPLE 3 Three 40 gram charges of a composition containing sodium azide, silicon and potassium perchlorate in molar proportions 8:4:3 were placed in canisters and ignited in a field test using a No. 8 electric blasing cap to initiate ignition. The material burned extremely quickly at a rate only fractionally less than a detonation.

EXAMPLE 4 One 20 gram charge of the composition in Example 3 was ignited in a field test, by means of an S1 19 squib. The material required about 2 seconds for complete combustion.

EXAMPLE 5 Two 5 gram charges of the material in Example 3 were placed in canisters and ignited in a closed high pressure vessel. Ignition was achieved by means of a hot wire. A peak pressure of approximately 900 psi. was achieved in 22 milliseconds after the initiation of combustion.

The solid products of two combustion experiments were recovered and analysed. The results indicated that 97 percent of the silicon metal had been converted in a water soluble silicate.

EXAMPLE 6 Two 20 gram charges of the material in Example 3 were placed in canisters and ignited in a closed high pressure vessel. Ignition was by means of a hot wire. A peak pressure of approximately 9,000 p.s.i. was achieved in l 1 milliseconds after initiation of combustion.

EXAMPLE 7 Five 20 gram charges of material in Example 1 were placed in canisters and ignited in a closed pressure vessel by means of a hot wire. A peak pressure of 2,500 p.s.i. was achieved in a combustion time of milliseconds. Some ignition delay was observed using the hot wire method of ignition. The above figure of 110 milliseconds is actual burn time, and does not include the delay period.

The solid products of combustion of three of these ignitions were collected and analysed. Analysis indicated that 87% of the silica originally present in the propellant had been converted to a water soluble silicate.

EXAMPLE 8 Three 20 gram charges of a composition containing sodium azide, aluminum and potassium chlorate in the molar proportions 2:2:1 were placed in canisters and ignited in a closed high pressure vessel. ignition was by means of a hot wire. The samples had an average combustion time of 14 milliseconds. The residue of combustion was extracted with water and the water extract analyzed for sodium and aluminum. The atomic ratio Al/Na is given in table 1. it can be seen that the conversion of aluminum into sodium aluminate NaA1O is on average 52 percent efficient, since complete conversion would provide a Al/Na ratio of 1.0.

EXAMPLE 9 Three 20 gram charges of a composition containing sodium azide. alumina (A1 0 and potassium perchlorate in the molar proportions 8:4:l were placed in canisters and ignited in a closed high pressure vessel. Ignition was by means of a hot wire. The samples had an average combustion time of milliseconds. The residue was analyzed as in Example 8. The results are given in Table 1. It can be seen that the conversion into sodium aluminate is on average 48 percent efficient.

TABLE] Atomic Ratio Al/Na Average Al/Na Example 8 Example 9 EXAMPLE 10 The effect of a hydrophobic silica ingredient on the sensitivity of the following compositions; sodium azide, silicon, potassium perchlorate in molar ratio 814:3 and sodium azide, silicon dioxide, potassium perchlorate in molar ratio 8:4:] was measured by adding to the compositions an additional 2 percent by weight of the following materials:

1. fumed silica having a silane coating (Silanox 101) Silanox is a registered trade mark. Silanox 101 has a surface area of 225 sq. meters/gram and a pH of 2. precipitated silica coated with polysiloxane.

a. QUSO WR 50 b. QUSO WR 82 QUSO is a registered trade mark. WRSO has a surface area of 130 sq. meters/gram and a pH of 8.5. WR 82 has a surface area of 120 sq. meters/gram and a pH of 11.0.

The sensitivity was measured with a drop hammer using the height at which zero ignition occurred in 20 drop tests. The results are shown in TABLE II.

It can be seen that fumed silica coated with a silane acts as a desensitizer.

What we claim is:

l. A. gas generating composition comprising a mixture of particles of the following ingredients 1. an alkali metal azide or an alkaline earth metal azide,

2. an oxidizing compound in proportion sufficient to react completely with said azide with the liberation of nitrogen therefrom, and

3. an oxide selected from the group consisting of silicon dioxide, aluminum oxide, titanium dioxide, tin oxide and zinc oxide, with or without admixture with a metal selected from the group consisting of silicon, aluminum, tin and Zinc, said oxide and metal being in proportion sufficient to react with all the metallic residue of the reaction between l and (2).

2. A gas generating composition as claimed in claim 1 wherein the azide is selected from the group consisting of lithium azide, sodium azide, potassium azide, rubidium azide, cesium azide, calcium azide, magnesium azide, strontium azide and barium azide.

3. A gas generating composition as claimed in claim 1 wherein the oxidizing compound is a metal peroxide selected from the group consisting of sodium peroxide, potassium peroxide, rubidium peroxide, cesium peroxide, calcium peroxide, strontium peroxide and barium peroxide.

4. A gas generating composition as claimed in claim 1 wherein the oxidizing compound is an inorganic perchlorate selected from the group consisting of lithium perchlorate, sodium perchlorate, potassium perchlorate, rubidium perchlorate, magnesium perchlorate, calcium perchlorate, strontium perchlorate, barium perchlorate, ferric perchlorate and cobalt perchlorate.

5. A gas generating composition as claimed in claim 1 wherein the oxidizing compound is a metal nitrate selected from the group consisting of lithium nitrate, sodium nitrate, potassium nitrate, copper nitrate, silver nitrate, magnesium nitrate, barium nitrate, zinc nitrate, aluminum nitrate, thallium nitrate, stannic nitrate, bismuth nitrate, manganese nitrate, ferric nitrate, ferrous nitrate and nickel nitrate.

6. A gas generating composition as claimed in claim 1 including as ingredient fumed silica coated with a water repellent.

7. A gas generating composition as claimed in claim 6 wherein the water repellant is a silane.

8. A gas generating composition as claimed in claim 6 wherein the fumed silica ingredient comprises 2% by weight of the composition. 

1. A GAS GENERATING COMPOSITION COMPRISING A MIXTURE OF PARTICLES OF THE FOLLOWING INGREDIENTS
 1. AN ALKALI METAL AZIDE OR AN ALKALINE EARTH METAL AZIDDE,
 2. AN OXIDIZING COMPOUND IN PROPORTION SUFFICIENT TO REACT COMPLETELY WITH SAID AZIDE WITH THE LIBERATION OF NITROGEN THEREFROM, AND
 2. A gas generating composition as claimed in claim 1 wherein the azide is selected from the group consisting of lithium azide, sodium azide, potassium azide, rubidium azide, cesium azide, calcium azide, magnesium azide, strontium azide and barium azide.
 2. an oxidizing compound in proportion suffiCient to react completely with said azide with the liberation of nitrogen therefrom, and
 3. an oxide selected from the group consisting of silicon dioxide, aluminum oxide, titanium dioxide, tin oxide and zinc oxide, with or without admixture with a metal selected from the group consisting of silicon, aluminum, tin and zinc, said oxide and metal being in proportion sufficient to react with all the metallic residue of the reaction between (1) and (2).
 3. A gas generating composition as claimed in claim 1 wherein the oxidizing compound is a metal peroxide selected from the group consisting of sodium peroxide, potassium peroxide, rubidium peroxide, cesium peroxide, calcium peroxide, strontium peroxide and barium peroxide.
 3. AN OXIDE SELECTED FROM THE GROUP CONSISTING OF SILICON DIOXIDE, ALUMINUM OXIDE, TITANIUM DIOXIDE, TIN OXIDE AND ZINC OXIDE, WITH OR WITHOUT ADMIXTURE WITH A METAL SELECTED FROM THE GROUP CONSISTING OF SILICON, ALUMINUM, TIN AND ZINC, SAID OXIDE AND METAL BEING IN PROPORTION SUFFICIENT TO REACT WITH ALL THE METALLIC RESIDUE OF THE REACTION BETWEEN (1) ANS (2).
 4. A gas generating composition as claimed in claim 1 wherein the oxidizing compound is an inorganic perchlorate selected from the group consisting of lithium perchlorate, sodium perchlorate, potassium perchlorate, rubidium perchlorate, magnesium perchlorate, calcium perchlorate, strontium perchlorate, barium perchlorate, ferric perchlorate and cobalt perchlorate.
 5. A gas generating composition as claimed in claim 1 wherein the oxidizing compound is a metal nitrate selected from the group consisting of lithium nitrate, sodium nitrate, potassium nitrate, copper nitrate, silver nitrate, magnesium nitrate, barium nitrate, zinc nitrate, aluminum nitrate, thallium nitrate, stannic nitrate, bismuth nitrate, manganese nitrate, ferric nitrate, ferrous nitrate and nickel nitrate.
 6. A gas generating composition as claimed in claim 1 including as ingredient fumed silica coated with a water repellent.
 7. A gas generating composition as claimed in claim 6 wherein the water repellant is a silane.
 8. A gas generating composition as claimed in claim 6 wherein the fumed silica ingredient comprises 2% by weight of the composition. 